Known methods of fabricating closely fitting, low friction, low wear machine parts include the steps of casting a self-lubricating composite material against a mating part. For example, a journal bearing can be fabricated by casting an epoxy containing a dry lubricant such as graphite against a polished shaft which has been coated with a parting compound for facilitating separation of the parts following hardening of the epoxy/lubricant mixture. After the epoxy has cured into a hard solid, the bearing can be broken loose from the shaft and worked with a lapping compound so that it passes freely over the shaft but has a very narrow clearance. When the shaft and bearing are washed free of the lapping compound, the resulting couple displays low friction and low wear rates.
The friction and wear of the bearing can be reduced still further by applying a dry lubricant coating to the shaft, usually by spraying and baking. Despite the reduction of friction and wear attained through application of the dry lubricant coating to the shaft, however, serious disadvantages attend its use. If the dry lubricant coating is applied following the lapping operation, the clearance of the two mated parts is changed. The resulting fit will either be too tight or too overlapped to provide allowance for the drylubricant coating is applied prior to the lapping step, most of the coating will be worn away by the abrasive lapping compound so that its friction-and wear-reducing effect is diminished or removed.
Therefore, there is a need for machine parts and methods of forming mated machine parts which exhibit close fit in combination but which are significantly less susceptible to friction and wear than currently available combinations of machine parts.
Accordingly, it is an object of the present invention to provide low friction, low wear, self-lubricating machine part combinations such as shaft/rotary bearing combinations, shaft/linear bearing combinations, screw/nut combinations and the like, and methods for making the same.
Another object of the invention is to provide machine member combinations useful in a wide range of environmental conditions.
Yet another object of the invention is to provide machine member combinations of high precision which exhibit low friction and wear under continuous, extended, industrial use.